dhcp.c

《嵌入式网络系统设计-基于Atmel ARM7 系列》这个本书的光盘资料

/**
 * @file
 *
 * Dynamic Host Configuration Protocol client
 */

/*
 *
 * Copyright (c) 2001-2004 Leon Woestenberg <[e-mail]>
 * Copyright (c) 2001-2004 Axon Digital Design B.V., The Netherlands.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * This file is a contribution to the lwIP TCP/IP stack.
 * The Swedish Institute of Computer Science and Adam Dunkels
 * are specifically granted permission to redistribute this
 * source code.
 *
 * Author: Leon Woestenberg <[e-mail]>
 *
 * This is a DHCP client for the lwIP TCP/IP stack. It aims to conform
 * with RFC 2131 and RFC 2132.
 *
 * TODO:
 * - Proper parsing of DHCP messages exploiting file/sname field overloading.
 * - Add JavaDoc style documentation (API, internals).
 * - Support for interfaces other than Ethernet (SLIP, PPP, ...)
 *
 * Please coordinate changes and requests with Leon Woestenberg
 * <[e-mail]>
 *
 * Integration with your code:
 *
 * In lwip/dhcp.h
 * #define DHCP_COARSE_TIMER_SECS (recommended 60 which is a minute)
 * #define DHCP_FINE_TIMER_MSECS (recommended 500 which equals TCP coarse timer)
 *
 * Then have your application call dhcp_coarse_tmr() and
 * dhcp_fine_tmr() on the defined intervals.
 *
 * dhcp_start(struct netif *netif);
 * starts a DHCP client instance which configures the interface by
 * obtaining an IP address lease and maintaining it.
 *
 * Use dhcp_release(netif) to end the lease and use dhcp_stop(netif)
 * to remove the DHCP client.
 *
 */
 
#include <string.h>
 
#include "lwip/stats.h"
#include "lwip/mem.h"
#include "lwip/udp.h"
#include "lwip/ip_addr.h"
#include "lwip/netif.h"
#include "lwip/inet.h"
#include "netif/etharp.h"

#include "lwip/sys.h"
#include "lwip/opt.h"
#include "lwip/dhcp.h"

#if LWIP_DHCP /* don't build if not configured for use in lwipopt.h */

/** global transaction identifier, must be
 *  unique for each DHCP request. We simply increment, starting
 *  with this value (easy to match with a packet analyzer) */
static u32_t xid = 0xABCD0000;

/** DHCP client state machine functions */
static void dhcp_handle_ack(struct netif *netif);
static void dhcp_handle_nak(struct netif *netif);
static void dhcp_handle_offer(struct netif *netif);

static err_t dhcp_discover(struct netif *netif);
static err_t dhcp_select(struct netif *netif);
static void dhcp_check(struct netif *netif);
static void dhcp_bind(struct netif *netif);
static err_t dhcp_decline(struct netif *netif);
static err_t dhcp_rebind(struct netif *netif);
static void dhcp_set_state(struct dhcp *dhcp, u8_t new_state);

/** receive, unfold, parse and free incoming messages */
static void dhcp_recv(void *arg, struct udp_pcb *pcb, struct pbuf *p, struct ip_addr *addr, u16_t port);
static err_t dhcp_unfold_reply(struct dhcp *dhcp);
static u8_t *dhcp_get_option_ptr(struct dhcp *dhcp, u8_t option_type);
static u8_t dhcp_get_option_byte(u8_t *ptr);
#if 0
static u16_t dhcp_get_option_short(u8_t *ptr);
#endif
static u32_t dhcp_get_option_long(u8_t *ptr);
static void dhcp_free_reply(struct dhcp *dhcp);

/** set the DHCP timers */
static void dhcp_timeout(struct netif *netif);
static void dhcp_t1_timeout(struct netif *netif);
static void dhcp_t2_timeout(struct netif *netif);

/** build outgoing messages */
/** create a DHCP request, fill in common headers */
static err_t dhcp_create_request(struct netif *netif);
/** free a DHCP request */
static void dhcp_delete_request(struct netif *netif);
/** add a DHCP option (type, then length in bytes) */
static void dhcp_option(struct dhcp *dhcp, u8_t option_type, u8_t option_len);
/** add option values */
static void dhcp_option_byte(struct dhcp *dhcp, u8_t value);
static void dhcp_option_short(struct dhcp *dhcp, u16_t value);
static void dhcp_option_long(struct dhcp *dhcp, u32_t value);
/** always add the DHCP options trailer to end and pad */
static void dhcp_option_trailer(struct dhcp *dhcp);

/**
 * Back-off the DHCP client (because of a received NAK response).
 *
 * Back-off the DHCP client because of a received NAK. Receiving a
 * NAK means the client asked for something non-sensible, for
 * example when it tries to renew a lease obtained on another network.
 *
 * We back-off and will end up restarting a fresh DHCP negotiation later.
 *
 * @param state pointer to DHCP state structure
 */
static void dhcp_handle_nak(struct netif *netif) {
  struct dhcp *dhcp = netif->dhcp;
  u16_t msecs = 10 * 1000;
  LWIP_DEBUGF(DHCP_DEBUG | DBG_TRACE | 3, ("dhcp_handle_nak(netif=%p) %c%c%"U16_F"\n", 
    (void*)netif, netif->name[0], netif->name[1], (u16_t)netif->num));
  dhcp->request_timeout = (msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS;
  LWIP_DEBUGF(DHCP_DEBUG | DBG_TRACE | DBG_STATE, ("dhcp_handle_nak(): set request timeout %"U16_F" msecs\n", msecs));
  dhcp_set_state(dhcp, DHCP_BACKING_OFF);
}

/**
 * Checks if the offered IP address is already in use.
 *
 * It does so by sending an ARP request for the offered address and
 * entering CHECKING state. If no ARP reply is received within a small
 * interval, the address is assumed to be free for use by us.
 */
static void dhcp_check(struct netif *netif)
{
  struct dhcp *dhcp = netif->dhcp;
  err_t result;
  u16_t msecs;
  LWIP_DEBUGF(DHCP_DEBUG | DBG_TRACE | 3, ("dhcp_check(netif=%p) %c%c\n", (void *)netif, (s16_t)netif->name[0],
    (s16_t)netif->name[1]));
  /* create an ARP query for the offered IP address, expecting that no host
     responds, as the IP address should not be in use. */
  result = etharp_query(netif, &dhcp->offered_ip_addr, NULL);
  if (result != ERR_OK) {
    LWIP_DEBUGF(DHCP_DEBUG | DBG_TRACE | 2, ("dhcp_check: could not perform ARP query\n"));
  }
  dhcp->tries++;
  msecs = 500;
  dhcp->request_timeout = (msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS;
  LWIP_DEBUGF(DHCP_DEBUG | DBG_TRACE | DBG_STATE, ("dhcp_check(): set request timeout %"U16_F" msecs\n", msecs));
  dhcp_set_state(dhcp, DHCP_CHECKING);
}

/**
 * Remember the configuration offered by a DHCP server.
 *
 * @param state pointer to DHCP state structure
 */
static void dhcp_handle_offer(struct netif *netif)
{
  struct dhcp *dhcp = netif->dhcp;
  /* obtain the server address */
  u8_t *option_ptr = dhcp_get_option_ptr(dhcp, DHCP_OPTION_SERVER_ID);
  LWIP_DEBUGF(DHCP_DEBUG | DBG_TRACE | 3, ("dhcp_handle_offer(netif=%p) %c%c%"U16_F"\n",
    (void*)netif, netif->name[0], netif->name[1], (u16_t)netif->num));
  if (option_ptr != NULL)
  {
    dhcp->server_ip_addr.addr = htonl(dhcp_get_option_long(&option_ptr[2]));
    LWIP_DEBUGF(DHCP_DEBUG | DBG_STATE, ("dhcp_handle_offer(): server 0x%08"X32_F"\n", dhcp->server_ip_addr.addr));
    /* remember offered address */
    ip_addr_set(&dhcp->offered_ip_addr, (struct ip_addr *)&dhcp->msg_in->yiaddr);
    LWIP_DEBUGF(DHCP_DEBUG | DBG_STATE, ("dhcp_handle_offer(): offer for 0x%08"X32_F"\n", dhcp->offered_ip_addr.addr));

    dhcp_select(netif);
  }
}

/**
 * Select a DHCP server offer out of all offers.
 *
 * Simply select the first offer received.
 *
 * @param netif the netif under DHCP control
 * @return lwIP specific error (see error.h)
 */
static err_t dhcp_select(struct netif *netif)
{
  struct dhcp *dhcp = netif->dhcp;
  err_t result;
  u32_t msecs;
  LWIP_DEBUGF(DHCP_DEBUG | DBG_TRACE | 3, ("dhcp_select(netif=%p) %c%c%"U16_F"\n", (void*)netif, netif->name[0], netif->name[1], (u16_t)netif->num));

  /* create and initialize the DHCP message header */
  result = dhcp_create_request(netif);
  if (result == ERR_OK)
  {
    dhcp_option(dhcp, DHCP_OPTION_MESSAGE_TYPE, DHCP_OPTION_MESSAGE_TYPE_LEN);
    dhcp_option_byte(dhcp, DHCP_REQUEST);

    dhcp_option(dhcp, DHCP_OPTION_MAX_MSG_SIZE, DHCP_OPTION_MAX_MSG_SIZE_LEN);
    dhcp_option_short(dhcp, 576);

    /* MUST request the offered IP address */
    dhcp_option(dhcp, DHCP_OPTION_REQUESTED_IP, 4);
    dhcp_option_long(dhcp, ntohl(dhcp->offered_ip_addr.addr));

    dhcp_option(dhcp, DHCP_OPTION_SERVER_ID, 4);
    dhcp_option_long(dhcp, ntohl(dhcp->server_ip_addr.addr));

    dhcp_option(dhcp, DHCP_OPTION_PARAMETER_REQUEST_LIST, 4/*num options*/);
    dhcp_option_byte(dhcp, DHCP_OPTION_SUBNET_MASK);
    dhcp_option_byte(dhcp, DHCP_OPTION_ROUTER);
    dhcp_option_byte(dhcp, DHCP_OPTION_BROADCAST);
    dhcp_option_byte(dhcp, DHCP_OPTION_DNS_SERVER);

    dhcp_option_trailer(dhcp);
    /* shrink the pbuf to the actual content length */
    pbuf_realloc(dhcp->p_out, sizeof(struct dhcp_msg) - DHCP_OPTIONS_LEN + dhcp->options_out_len);

    /* TODO: we really should bind to a specific local interface here
       but we cannot specify an unconfigured netif as it is addressless */
    udp_bind(dhcp->pcb, IP_ADDR_ANY, DHCP_CLIENT_PORT);
    /* send broadcast to any DHCP server */
    udp_connect(dhcp->pcb, IP_ADDR_BROADCAST, DHCP_SERVER_PORT);
    udp_send(dhcp->pcb, dhcp->p_out);
    /* reconnect to any (or to server here?!) */
    udp_connect(dhcp->pcb, IP_ADDR_ANY, DHCP_SERVER_PORT);
    dhcp_delete_request(netif);
    LWIP_DEBUGF(DHCP_DEBUG | DBG_TRACE | DBG_STATE, ("dhcp_select: REQUESTING\n"));
    dhcp_set_state(dhcp, DHCP_REQUESTING);
  } else {
    LWIP_DEBUGF(DHCP_DEBUG | DBG_TRACE | 2, ("dhcp_select: could not allocate DHCP request\n"));
  }
  dhcp->tries++;
  msecs = dhcp->tries < 4 ? dhcp->tries * 1000 : 4 * 1000;
  dhcp->request_timeout = (msecs + DHCP_FINE_TIMER_MSECS - 1) / DHCP_FINE_TIMER_MSECS;
  LWIP_DEBUGF(DHCP_DEBUG | DBG_STATE, ("dhcp_select(): set request timeout %"U32_F" msecs\n", msecs));
  return result;
}

/**
 * The DHCP timer that checks for lease renewal/rebind timeouts.
 *
 */
void dhcp_coarse_tmr()
{
  struct netif *netif = netif_list;
  LWIP_DEBUGF(DHCP_DEBUG | DBG_TRACE, ("dhcp_coarse_tmr()\n"));
  /* iterate through all network interfaces */
  while (netif != NULL) {
    /* only act on DHCP configured interfaces */
    if (netif->dhcp != NULL) {
      /* timer is active (non zero), and triggers (zeroes) now? */
      if (netif->dhcp->t2_timeout-- == 1) {
        LWIP_DEBUGF(DHCP_DEBUG | DBG_TRACE | DBG_STATE, ("dhcp_coarse_tmr(): t2 timeout\n"));
        /* this clients' rebind timeout triggered */
        dhcp_t2_timeout(netif);
      /* timer is active (non zero), and triggers (zeroes) now */
      } else if (netif->dhcp->t1_timeout-- == 1) {
        LWIP_DEBUGF(DHCP_DEBUG | DBG_TRACE | DBG_STATE, ("dhcp_coarse_tmr(): t1 timeout\n"));
        /* this clients' renewal timeout triggered */
        dhcp_t1_timeout(netif);
      }
    }
    /* proceed to next netif */
    netif = netif->next;
  }
}

/**
 * DHCP transaction timeout handling
 *
 * A DHCP server is expected to respond within a short period of time.
 * This timer checks whether an outstanding DHCP request is timed out.
 * 
 */
void dhcp_fine_tmr()
{
  struct netif *netif = netif_list;
  /* loop through netif's */
  while (netif != NULL) {
    /* only act on DHCP configured interfaces */
    if (netif->dhcp != NULL) {
      /* timer is active (non zero), and is about to trigger now */      
      if (netif->dhcp->request_timeout > 1) {
        netif->dhcp->request_timeout--;
      }
      else if (netif->dhcp->request_timeout == 1) {
        netif->dhcp->request_timeout--;
        /* { netif->dhcp->request_timeout == 0 } */
        LWIP_DEBUGF(DHCP_DEBUG | DBG_TRACE | DBG_STATE, ("dhcp_fine_tmr(): request timeout\n"));
        /* this clients' request timeout triggered */
        dhcp_timeout(netif);
      }
    }
    /* proceed to next network interface */
    netif = netif->next;
  }
}

/**
 * A DHCP negotiation transaction, or ARP request, has timed out.
 *
 * The timer that was started with the DHCP or ARP request has
 * timed out, indicating no response was received in time.
 *
 * @param netif the netif under DHCP control
 *
 */
static void dhcp_timeout(struct netif *netif)
{
  struct dhcp *dhcp = netif->dhcp;
  LWIP_DEBUGF(DHCP_DEBUG | DBG_TRACE | 3, ("dhcp_timeout()\n"));
  /* back-off period has passed, or server selection timed out */
  if ((dhcp->state == DHCP_BACKING_OFF) || (dhcp->state == DHCP_SELECTING)) {
    LWIP_DEBUGF(DHCP_DEBUG | DBG_TRACE, ("dhcp_timeout(): restarting discovery\n"));
    dhcp_discover(netif);
  /* receiving the requested lease timed out */
  } else if (dhcp->state == DHCP_REQUESTING) {
    LWIP_DEBUGF(DHCP_DEBUG | DBG_TRACE | DBG_STATE, ("dhcp_timeout(): REQUESTING, DHCP request timed out\n"));
    if (dhcp->tries <= 5) {
      dhcp_select(netif);
    } else {
      LWIP_DEBUGF(DHCP_DEBUG | DBG_TRACE | DBG_STATE, ("dhcp_timeout(): REQUESTING, releasing, restarting\n"));
      dhcp_release(netif);
      dhcp_discover(netif);
    }
  /* received no ARP reply for the offered address (which is good) */
  } else if (dhcp->state == DHCP_CHECKING) {
    LWIP_DEBUGF(DHCP_DEBUG | DBG_TRACE | DBG_STATE, ("dhcp_timeout(): CHECKING, ARP request timed out\n"));
    if (dhcp->tries <= 1) {
      dhcp_check(netif);
    /* no ARP replies on the offered address,
       looks like the IP address is indeed free */
    } else {
      /* bind the interface to the offered address */
      dhcp_bind(netif);
    }